Prescription eyeglass lenses are curved in such a way that light is correctly focused onto the retina of a patient's eye, improving vision. Such lenses are formed from glass or plastic lens “blanks” having certain desired properties to provide the correct prescription for the patient. The blanks are usually circular and of substantially larger dimension, for example 70 mm in diameter, compared to the relatively smaller finished lenses assembled into eyeglass frames. Therefore, a lens blank must be edged to fit an eyeglass frame selected by the patient.
Ophthalmic laboratory technicians cut, grind, edge, and polish blanks according to prescriptions provided by dispensing opticians, optometrists, or ophthalmologists. The specifications include the patient's full prescription, including: 1) the total power the finished lens must have; 2) the strength and size of any segments, if needed (i.e. multifocal lenses); 3) the power and orientation of any cylinder curves; and 4) the location of the optical center and any inducted prism that may be needed. The optical center is the spot on the eyeglass lens where light passes through without refracting, and is normally placed in front of the patient's pupil.
In addition, the large diameter blank is sized and shaped to fit into the frame selected by the patient. The lens blank may be shaped using an edger, such as the edger disclosed in U.S. Pat. No. 6,203,409 to Kennedy et al., the disclosure of which is incorporated herein by reference. The blank is edged so that the periphery of the finished lenses fit into the openings on the frames.
Edging of a lens blank typically requires the application of a block to a surface thereof. The block is releasably secured to a clamp assembly, so that rotation of the clamp assembly causes corresponding rotation of the lens blank. As the blank is rotated, the periphery of the blank may be cut to a desired size using a router tool. The lens periphery may also be polished using a polishing tool. A bevel or groove is often formed about the lens.
The finished lens may then be assembled with the selected eyeglass frames. The frames include two spaced openings in which the finished lenses are mounted. Many frames have a bevel extending around the inner circumference of the openings. The bevel interlocks with a complementarily shaped groove formed about the peripheral edge of the lens. The interlock between the complementary bevel and groove helps to secure the lens within the opening.
Information relating to the size and shape of the lens needed for a particular frame (i.e. trace data) may be generated, and subsequently transmitted to the edger. Such trace data may be generated by a tracer machine, which includes a clamp assembly for clamping the frames in place, and an engager having a projecting surface for tracing the groove of the frames. Trace data is thereby generated according to the position of the engager. The trace data may be stored in a control system, such as a central processing unit, in communication with the edger.
The edger processes the edge of the lens blank to create an edge profile according to the trace data. A router tool on the edger forms the groove about the lens. The router tool may include a grooving wheel for forming the groove. During the edging and grooving process, lens material debris is generated and often remains in the groove being formed. This debris, or “lens trash”, must be manually removed by the lab technician after the edging process, thereby increasing manufacturing time and cost.